1. Field of the Invention
The invention relates in general to the field of electrical component manufacturing, and specifically to a process for tinning electrical leads.
2. Description of the Related Art
Brush blocks used in gyroscopes and synchro type electric motors can be connected electrically and mechanically by using molded-in lead wires or terminals. The terminals are frequently flat plate brass (or some other base metal), on the order of 0.015xe2x80x3 thick and are typically plated with a material which promises better oxidation protection and thus better solderability than bare brass or BeCu. Popular plating materials include tin and silver. Unfortunately however, the tin plating eventually tends to oxidize, thus reducing the possibility of long term shelf storage. Silver also tends to develop a sulfide complex coating (e.g. such as the black tarnish seen on silver-plated dining ware), thus causing the terminals to be virtually unsolderable.
Thus, a common solution is to xe2x80x9ctinxe2x80x9d the terminals over the plating using a hot tin-lead solder dip, typically Sn63 (Pb37). The difference in solderability between a hot solder dipped terminal and a plated terminal is quite significant. Despite the advantages of hot solder dipping however, there remain undesirable effects. In the case of a flat plate terminal with a small diameter through hole (typically 0.040xe2x80x3) which will later receive a wire, hot solder dipping results in partial, if not complete occlusion of the hole by solder. This solder-filled hole is typically too small to receive the wire for which the hole was intended. Of course, the additional solder could be drilled out, however this adds a costly processing step, and may potentially produce an inordinate number of rejected parts. Thus it is desirable to create a solder tinning process in which solder is prevented from occluding holes in a flat terminals during hot solder dipping.
Thus, in one embodiment, a method of hot solder dipping an electrical terminal is disclosed. According to this embodiment, an electrical terminal having a through hole for receiving a wire is provided. The method further includes positioning a solder resistant material through the hole, immersing at least a portion of the terminal in hot solder, and removing the solder resistant material from the through hole.
According to another embodiment, a method of tinning an electrical terminal is disclosed. This embodiment includes providing an electrical terminal having a hole sized to receive a lead wire of a first diameter. Additionally, the method includes providing a solder resistant filament having a second diameter such that the second diameter is at least equal to the first diameter. The solder resistant filament is inserted through the hole, at least a portion of the terminal is submerged in molted solder, and the solder resistant filament is withdrawn from the hole.
In yet another embodiment, a method of tinning a plurality of electrical terminals is provided. The method includes providing a plurality of electrical terminals with through holes. The method further includes inserting a single solder resistant wire through the holes of said plurality of terminals and immersing the plurality of terminals in molten solder such that a layer of solder is deposited on the terminals. After a desired dwell time, the terminals are removed from the solder, and the wire is removed from the terminals.
For purposes of summarizing the invention and the advantages achieved over the prior art, certain objects and advantages of the invention have been described herein above. Of course, it is to be understood that not necessarily all such objects or advantages may be achieved in accordance with any particular embodiment of the invention. Thus, for example, those skilled in the art will recognize that the invention may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other objects or advantages as may be taught or suggested herein.
All of these embodiments are intended to be within the scope of the present invention herein disclosed. These and other embodiments of the present invention will become readily apparent to those skilled in the art from the following detailed description of the preferred embodiments having reference to the attached figures, the invention not being limited to any particular preferred embodiment(s) disclosed.